Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA.
Photochem Photobiol. 2022 Mar;98(2):303-310. doi: 10.1111/php.13531. Epub 2021 Dec 2.
Polymethine fluorophores have facilitated the advance of biological and material sciences, due to their advantageous photophysical properties. However, the need to maintain a monomeric state can severely limit the utility and processability of dyes. High concentrations of fluorophore can lead to aggregation and negate the beneficial photophysical properties of monomers. Another concern is "crossing the cyanine limit" in which delocalization within the polymethine scaffold is broken, producing the presence of an asymmetric state diminishing its photophysical behavior. Herein, we attempt to overcome these limitations by exploring anion exchange on a cationic flavylium heptamethine scaffold. By increasing the size and hydrophobicity of the anion, we can effectively tune the degree of ion pairing within the polymethine dye. Interestingly, we found that the effect of ion pairing on photophysical properties was subtle for the flavylium heptamethine scaffold in comparison to the more commonly used indolenine cyanine dye. Utilizing larger weakly coordinating anions enabled solubility of the flavylium heptamethine fluorophore in nonpolar solvents, which could otherwise not be achieved. Even with more subtle effects than classic cyanine dyes, anion exchange on flavylium polymethine dyes holds potential for further manipulation of the properties of these low energy dyes.
多甲川荧光染料由于其有利的光物理性质，促进了生物和材料科学的发展。然而，维持单体状态的需求会严重限制染料的实用性和可加工性。荧光染料的高浓度会导致聚集，从而否定单体的有益光物理性质。另一个关注点是“超越花菁极限”，其中多甲川骨架内的离域被打破，产生不对称状态，降低其光物理行为。在此，我们试图通过探索阳离子 flavylium 七甲川骨架上的阴离子交换来克服这些限制。通过增加阴离子的尺寸和疏水性，我们可以有效地调节多甲川染料内的离子对程度。有趣的是，我们发现与更常用的吲哚啉花菁染料相比，离子对对于 flavylium 七甲川骨架的光物理性质的影响很小。利用较大的弱配位阴离子可以使 flavylium 七甲川荧光染料在非极性溶剂中具有溶解性，否则无法实现。即使与经典花菁染料相比，阴离子交换在 flavylium 多甲川染料上具有进一步操纵这些低能量染料性质的潜力。
